This research involves the isolation and characterization of liver aldehyde and xanthine oxidases from a number of different strains of mice. Its purpose is to understand how these enzymes function both biochemically and physiologically and to determine if there is an evolutionary connection between them. A significant emphasis in this work will be the acquisition of mutant forms of xanthine oxidase, through the mutagenesis of preimplantation embryos and screening by electrophoretic methods. Procedures for the purification of aldehyde and xanthine oxidases from small samples of liver will employ affinity chromatography.